A wide variety of surfactants have been described for use in the preparation of photographic materials.
JP56-19042 describes various diester sulfoitaconates as dispersing aids for photographic additives. The two ester linked hydrophobic groups include a number of substituted or unsbstituted alkyl or aryl groups.
U.S. Pat. No. 3,948,663 describes photographic materials containing certain sulfosuccinate surface active agents and refers to their possible use as dispersing aids and coating aids. A specific example of such a surface active agent is sodium dioctyl sulfosuccinate which is commercially available as Aerosol.TM.OT.
W093/03420 describes a method of making fine particle photographic coupler dispersions which comprises forming a dispersion of photographic coupler, coupler solvent and auxiliary coupler solvent in an aqueous gelatin medium containing at least about 1% by weight of an anionic surfactant having a hydrophobicity of 2-10 log P(OH) and washing the dispersion with water for a time sufficient to remove at least one fourth of the surfactant. Anionic surfactants of diverse structures may be employed and included among several named surfactants is diphenylbutyl sodium sulfosuccinate.
A shortcoming of the use of surfactants described in JP56-19042 and U.S. Pat. No. 3,948,663 is the very low surface tension values exhibited by the compounds at concentrations above their critical micelle concentration (CMC). In the simultaneous multilayer coating of hydrophilic colloid layers, it is essential that the surface tension of the top layer is lower than that of any of the underlying layers if it is to remain spread during the coating operation. If one of the underlying lavers has a lower surface tension than the top layer it drives the top layer in from the edges towards the centre of the coating. This is often termed "edge retraction". The larger the surface tension imbalance, the more disruptive is the effect. Large differences can cause retraction of the whole coating pack and general layer inversions. The surface tension of underlying layers in the multilayer coating of photographic materials is often dominated by the surfactant dispersing aid that is used to stabilize the emulsified hydrophobic particles therein e.g. colour couplers and their associated solvents.
When such prior art surfactants are used as dispersing aids for emulsified materials that are incorporated in underlying hydrophilic colloid layers during simultaneous multilayer coating, a constraint is put on the choice of surfactant or surfactant concentration required for the overlying layers i.e. coating latitude is relatively narrow.
Another shortcoming of the use of the surfactants described in JP56-19042 and U.S. Pat No. 3,948,663 as dispersing aids for photographic couplers in hydrophilic colloid compositions is that the photographic properties of such compositions e.g. the liquid dispersion reactivity, can be less than desired.
A further shortcoming of the use of the surfactants described in JP56-19042 and U.S. Pat. No. 3,948,663 as dispersing aids in photographic materials is that they can contribute to foaming during photographic processing, especially in seasoned developers where surfactants have leached out from the material and have built up in concentration.
Problem to be Solved by the Invention
The invention overcomes the coating latitude problem associated with the prior art dipersing aids.
Limitations in the photographic properties of dispersions of photographic couplers in hydrophilic colloids can be overcome.
The invention can reduce the foaming which can occur during the processing of photographic materials containing the prior art dispersing aids.